Brain changes that relate to sensory stimulation or deprivation are reasonably established. Whether those changes are primarily a consequence of direct or of indirect (tonic) activation is less clear. This research project seeks to compare brain development (cortical and cerebellar) and behavior in stumptail macaques reared under three degrees of somatosensory deprivation. Rearing conditions will be maintained under different time schedules to determine sensitive periods. Each level of deprivation will be compared also with a control condition in which species typical social stimulation occurs. Our hypotheses are: 1) brain development will be correlated with amount of somatosensory stimulation, 2) stimulation from the most enriched of the 3 experimental conditions will produce as much brain growth as the social environment, and 3) the visual cortex will reflect the same 3 levels of development as the somatosensory cortex, due to tonic variations in cortical activations. Brain areas will be compared across treatment conditions through measures of stellate and pyramidal cell diameters, densities, and dendritic growth and orientations. Behavioral measures are a series of daily observations on locomotor, approach, withdrawal, and stereotyped behaviors and a final battery of tests given at 6 months. Recent studies have uncovered species differences in mother-infant separation effects that limit somewhat the generality of findings on rhesus monkeys. This work on the stumptail will contribute to the understanding of mother-infant separation effects as well as elucidate the time course of behavioral changes and changes in the growth of sensory systems in the brain.